[ISSUE #7026] When there is no master, proxy method 'getBrokerAddr' should not return null, but the address of slave

[gaoyf]

Which Issue(s) This PR Fixes

Fixes #7026

Brief Description

When there is no master, method 'getBrokerAddr' should not return null, but the address of slave.

How Did You Test This Change?

[codecov-commenter]

Codecov Report

Merging #7027 (89e3a61) into develop (2246c32) will increase coverage by 0.03%. The diff coverage is 48.08%.

@@              Coverage Diff              @@
##             develop    #7027      +/-   ##
=============================================
+ Coverage      42.61%   42.64%   +0.03%     
- Complexity      9122     9236     +114     
=============================================
  Files           1128     1136       +8     
  Lines          80133    80643     +510     
  Branches       10432    10539     +107     
=============================================
+ Hits           34146    34388     +242     
- Misses         41706    41966     +260     
- Partials        4281     4289       +8     

Impacted Files	Coverage Δ
.../apache/rocketmq/filter/parser/ParseException.java	56.71% <ø> (+7.46%)	:arrow_up:
...ocketmq/filter/parser/SelectorParserConstants.java	100.00% <ø> (ø)
...pache/rocketmq/filter/parser/SimpleCharStream.java	37.94% <ø> (ø)
.../java/org/apache/rocketmq/filter/parser/Token.java	61.53% <ø> (ø)
...g/apache/rocketmq/filter/parser/TokenMgrError.java	0.00% <ø> (ø)
...etmq/filter/parser/SelectorParserTokenManager.java	47.26% <39.70%> (+0.23%)	:arrow_up:
.../apache/rocketmq/filter/parser/SelectorParser.java	46.64% <46.23%> (+6.53%)	:arrow_up:
...cketmq/filter/expression/ComparisonExpression.java	52.98% <73.33%> (+9.39%)	:arrow_up:
.../proxy/service/route/ClusterTopicRouteService.java	90.00% <100.00%> (+17.27%)	:arrow_up:
...rocketmq/proxy/service/route/MessageQueueView.java	64.70% <100.00%> (+2.20%)	:arrow_up:

... and 103 files with indirect coverage changes

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